Proton therapy is a type of external beam radiation therapy that is characterized by the use of a beam of protons to irradiate diseased tissue. A chief advantage of proton therapy over other conventional therapies such as X-ray or neutron radiation therapies is that proton radiation can be limited by depth, and therefore the exposure to inadvertent radiation can be avoided or at least limited by non-target cells having a depth beyond a target calculated area.
A popular implementation of proton therapy uses mono-energetic pencil beams at varying energy levels, which are spot-scanned over a target area for one or more layers of depth. By superposition of several proton beams of different energies, a Bragg peak can be spread out to cover target volumes using a uniform, prescribed dose. This enables proton radiation applications to more precisely localize the radiation dosage relative to other types of external beam radiotherapy. During proton therapy treatment, a particle accelerator such as a cyclotron or synchrotron is used to generate a beam of protons from, for example, an internal ion source located in the center of the particle accelerator. The protons in the beam are accelerated (via a generated electric field), and the beam of accelerated protons is subsequently “extracted” and magnetically directed through a series of interconnecting tubes (called a beamline), often through multiple chambers, rooms, or even floors of a building, before finally being applied through a radiation application device at an end section of beam line (often through a radiation nozzle) to a target volume in a treatment room.
As the volumes (e.g., organs, or regions of a body) targeted for radiation therapy are often below the surface of the skin and/or extend in three dimensions, and since proton therapy—like all radiation therapies—can be harmful to intervening tissue located in a subject between the target area and the beam emitter, the precise calculation and application of correct dosage amounts and positions are critical to avoid exposing regions in the radiation subject outside the specific areas targeted to receive radiation.
As a solution to this issue, radiation devices have been equipped with specialized computer-controlled hardware collimator devices, such as collimator jaws and multi-leaf collimators (MLCs), which control the shape and size of a beam application field. These devices have been developed to deliver fields conforming to the projection of the target with greater ease and accuracy. In more advanced applications, the collimator jaws and/or the individual leaves of an MLC are moved separately under computerized control systems at desired speeds during periods of radiation (e.g., beam-on). This has enabled the generation of spatially modulated radiation fields, since each leaf attenuates the beam for a different time period. The resulting intensity modulated proton therapy (IMPT) has allowed the application of high dose volumes that conform more closely to the shape of complicated targets.
However, while these developments allow programming of more accurate beam fields, the devices themselves are still subject to mechanical errors or measurement variances that may result in inaccuracies during radiation application. More generally, the devices were originally developed for photon radiation applications, which used a broader starting particle beam. The development of thin, spot-scanning pencil proton beams obviate much of the need for complicated beam field shaping components, which can be less optimized and cost-efficient to use. This is especially true for modern MLCs that can have tens of leaves and corresponding motors, making them extremely costly to manufacture and maintain, and complex. Moreover, typical jaw and MLC shapes are implemented with angularly shaped components (e.g., rectangular blocks and/or leaves) which can be ineffective to shape a beam field optimally to treat target areas with less sharp angles.
Another conventional solution involves using block apertures of a rigid material, shaped specifically to limit beam fields to a particular target area and for a particular radiation subject. Since these apertures are customized for each application, the time required to plan, produce, and install these devices can be extensive, and may not be suitable for time-sensitive applications. Moreover, use of subject and tumor-specific apertures require manual effort to change and swap out apertures in lieu of other apertures during beam applications at different depths or orientations, which can be time and user-intensive.